1. Field of the Invention (Technical Field)
The present invention relates generally to an apparatus and system for use with natural gas dehydrators of the type used to remove water and water vapor from a natural gas stream having a mixture of natural gas, liquid hydrocarbons, liquid hydrocarbon vapors, water and water vapors.
2. Description of Related Art
Note that the following discussion refers to a number of publications by author(s) and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
An example of natural gas dehydrators is disclosed in U.S. Pat. No. 6,238,461 issued May 29, 2001 and U.S. Pat. No. 6,364,933 issued Apr. 2, 2002 to Heath and the disclosures therein are specifically incorporated herein by reference. In general, such systems comprise a separator for receiving oil and water liquids from “wet” (water vapor laden) gas; and a water absorber, which employs a liquid dehydrating agent such as glycol, for removing the water vapor from the wet gas and producing “dry” gas suitable for commercial usage. The glycol is continuously supplied by a pump to the absorber in a “dry” low-water vapor-pressure condition and is removed from the absorber in a “wet” high-water vapor-pressure condition. The wet glycol is continuously removed from the absorber and circulated through a reboiler, which includes a still column for removing the absorbed water from the glycol and heating the glycol to provide a new supply of hot dry glycol. Heating of the glycol in the reboiler is generally accomplished through use of a gas burner mounted in a fire tube. The hot dry glycol from the reboiler passes through a heat exchanger, where the hot dry glycol transfers some of its heat to incoming wet glycol going to the still column. The dry glycol subsequently passes to a dry glycol storage tank. A glycol passage is provided to enable passage of wet glycol from the absorber to the reboiler and to pump dry glycol from a storage tank to the absorber. Besides water, the wet glycol going to the still column of the reboiler of the natural gas dehydrator will contain natural gas and absorbed hydrocarbons, and other gaseous components.
On many dehydrators, a volume of natural gas is intentionally induced into the reboiler in order to dry the wet glycol to a higher concentration than can be accomplished by simply adding heat. The process of intentionally inducing a volume of natural gas into the reboiler is referred to as gas stripping.
In the still column of the reboiler of the natural gas dehydrator, the water, natural gas, and other hydrocarbons are separated from the glycol by the pressure reduction from the absorber pressure to approximately atmospheric pressure in the still column and by the application of heat to the reboiler.
The water, natural gas, other hydrocarbons and gases contained in the wet glycol stream which are separated in the still column from the wet glycol are exhausted as vapors into the atmosphere through the atmospheric vent on the still column unless facilities are installed to collect and dispose of the vented vapors. The hydrocarbon vapors released through the still column of a natural gas dehydrator are air pollutants. Specifically, certain hydrocarbons such as benzene, toluene, ethylbenzene, and xylene, commonly referred to as BTEX have been proven to be carcinogenic. Other gases such as hydrogen sulfide, when present, are toxic.
The gas dehydrator and systems for use with gas dehydrators disclosed in U.S. Pat. Nos. 6,238,461, 5,766,313, 6,364,933, and Ser. No. 10/071,721, now issued U.S. Pat. No. 6,551,379, offer solutions to at least some of the problems discussed above. The present invention provides improvements to such gas dehydrators and systems.